U.S. Pat. Nos. 4,808,313; 4,944,881; and 4,985,147 to Mochizuki et al., issued Feb. 28, 1989; Jul. 31, 1990; and Jan. 15, 1991, respectively, all assigned to the Japanese Agency of Industrial Science and Technology teach the formation of a chitosan semi-permeable membrane and its use in separating water from various organic compounds. The reference does not teach or suggest that polysaccharide membranes could be useful in a process to separate olefins from paraffins, nor does the patent teach the process steps for the separation of olefins from paraffins using such a membrane.
U.S. Pat. No. 4,623,704 issued Nov. 18, 1986 to Dembicki et al., assigned to the Dow Chemical Company teaches passing a stream of gaseous ethane and ethylene from a solution polymerization through a semi permeable hollow fiber to remove ethylene from the feed and increase the concentration of ethylene in the permeate (i.e. alkene/alkane separation). The permeate is then recycled back to the polymerization reactor. The reference teaches a number of semi-permeable membranes and particularly cellulose esters such as the acetate, diacetate, and triacetate. The reference fails to teach the specific steps of the present invention including the removal of sulfur compounds, humidification of the feed stream with water, and the use of a demistifier to remove droplets from the feed stream. Additionally, the reference totally fails to teach chelating a silver or copper (I) (e.g. cuprous) metal compound in the semi-permeable membrane.
U.S. Pat. No. 5,034,134 issued Jul. 23, 1991 to George et al., assigned to Union Carbide Chemicals and Plastics Technology Corporation discloses the use of semi-permeable membranes to separate impurities and/or additives from a liquid stream comprising ethylene glycol and water. The patent does not teach separating alkenes from alkanes (paraffins) in a gas phase (e.g. pervaporation).
There are a number of patents in the name of Moll, assigned to the Dow Chemical Company that teach the separation of gases at low temperatures. Representative of this art are U.S. Pat. Nos. 5,352,272; 5,679,133; and 5,837,032. These patents teach the use of glassy polymers or rubbery polymers as the semi-permeable membrane. The references fail to teach the use of polysaccharides and in particular chitosan as the semi-permeable membrane.
There are a number of patents assigned to Membrane Technology and Research, Inc. including U.S. Pat. Nos. 6,271,319; 6,414,202; and 6,525,236. These patents also teach the separation of gases using rubbery or glassy polymers. U.S. Pat. No. 6,271,319 is of interest as it refers to the incorporation of silver ions to improve the transfer of propylene across the membrane.
U.S. Pat. No. 5,670,051 issued Sep. 27, 1997 to Pinnau et al., assigned to Membrane Technology and Research, Inc. discloses separating olefins from a stream containing other components using a membrane which is made from a polymer selected from the group consisting of rubbery polymers (e.g. silicon rubber), a polyalkyl oxide (e.g. poly (ethylene oxide)), polymers containing ether linkages (e.g. epihalohydrin or propylene oxide/allylglycidalether copolymer), polyetherpolyamide block copolymers and polyesters such as polyalkyl adipates, succinates sebacates and so on. The patent does not disclose or suggest the polysaccharide semi-permeable membranes of the present invention. Further the patent teaches the membrane is preferably used in a dry mode. The patent teaches that silver nitrate is not suitable as a material to incorporate into the membrane.
The present invention seeks to provide a relatively simple process to separate olefins, preferably C2-8 olefins, desirably alpha olefins, from C1-10 preferably C1-8 paraffins. The process is energy efficient and uses a polysaccharide membrane as the semi-permeable membrane preferably on a support membrane.